Interdigital magnetron



Dec. 0, 1955 P. R. FINGER INTERDIGITAL MAGNETRON Filed May 11, 1950INVENTOR. Paul RFmger United States Patent O INTERDIGITAL MAGNETRON PaulR. Finger, Cedar Rapids, Iowa, assignor to Collins Radio Company, CedarRapids, Iowa, a corporation of Iowa Application May 11, 1950, Serial No.161,387

3 Claims. c1. 31539.73)

This invention relates in general to inter-digital magnetrons, and inparticular to a magnetron which has liquidcooled fingers.

Inter-digital magnetrons have been used, but two adverse eilects arenoticed:

1. The fingers become too warm, and

2. The cathode couples a great deal of energy from the magnetron cavitydue to antenna action.

It is an object of this invention, therefore, to provide an interdigitalmagnetron which has liquid-cooled fingers.

A further object of this invention is to provide an interdigitalmagnetron which has shorting bars with polarities such as to counteractthe antenna effect of the center cathode.

Yet another object of this invention is to provide a magnetron which hasinter-digital members fluidly connected in an economical and practicalmanner.

A feature of this invention is found in the provision to an interdigitalmagnetron comprising a center cathode, an annular resonating anodestructure supported about the cathode, which has a meshing conduitsystem that serves as the inter-digital radio frequency inducingmembers.

Further objects, features, and advantages of this invention will becomeapparent from the following description and claims when read in view ofthe drawings, in which;

Figure 1 represents a cut-away view of the inter-digital magnetron ofthis invention showing the relative spatial relationship among thevarious parts;

Figure 2 is a sectional view taken on line 22 of Figure 1 illustratinghow the inter-digital members are spaced relative to each other; and,

Figure 3 is a detailed view of the indirectly heated cathode.

Figure 1 shows an inter-digital magnetron which has a portion cutaway soas to illustrate more clearly the internal structure of the tube. Anexternal air-tight cover of a generally cylindrical shape encloses thetube. A mag netic pole 11 extends through the top of the container-10and a second magnetic pole 12 extends through the bottom of thecontainer. Magnetic means, not shown, complete the magnetic circuitexternally of the container 10 between the poles 11 and 12. The pole 12is formed with an axial opening 15 through which extends a cathodesupport member 13. A suitable vacuum seal exists between the pole 12 andsupport 13. The upper end 14 of the cathode support is indirectly heatedby a heating coil, as shown in Figure 3, and furnishes the electronsupply for the tube. The support 13 is hollow and contains a rod 16which is insulated from and supported within the support 13. The rod 16terminates adjacent the upper end of the support 13 and a resistancemember 17 is connected between the rod 16 and the active portion 14. Anopening 18 is formed in the support member 13 within the confines of thecontainer 10 to allow the interior of the tube to be evacuated. The endmembers 16 and 13 are sealed by glass or other suitable material.

A generally hollow annular-shaped member 19 is sup ported within thecontainer and attached to the container walls by support means 21. Across section of the annular member 19 is of a generally U shape withthe open side of the U pointing toward the active portion 14 which formsthe cathode of the tube. A direct current potential is impressed betweenthe cathode 14 and the annular member 19. This may be accomplished byimpressing a high negative potential on the support 13 through anexternal circuit and by grounding the container 10 which may beelectrically connected to the annular member 19. This high directcurrent potential tends to accelerate electrons emitted from the cathode14 towards the annular member 19. A magnetic field is impressed betweenthe pole pieces 11 and 12, and thus the emitted electrons are acted uponby the magnetic and electric fields combined. The strengths of thefields are adjusted so that the electrons will have a generallyspiralling path from the cathode; some falling back into the cathode,while others reach the anode 19.

A plurality of inter-digital fingers are formed by the conduit meansillustrated in Figure 1. For illustrative purposes, a structure witheight fingers is shown, but it is to be understood that any number offingers may be used. One half of the fingers are attached to the upperedge 22 of the annular member 19, and the other half of the fingers areconnected to the lower surface 23 of the annular member 19. A fluidinlet conduit 24 is ring-shaped and supported within the container 10above the top surface 22. An outlet conduit 26 is also supported abovethe surface 22. Likewise, a second inlet pipe 27 is supported within thecontainer adjacent the wall 23 and a second outlet pipe 28 is supportedadjacent pipe 27. Connected to the inlet pipe 24 is a tube 29 whichbends down to contact the wall 22 and extends radially to the internalopening of the annular member 19. The tube 29 passes transversely downthe open side of the annular member 19 to a point beyond the end wall23, but it does not contact the wall 23. A chord 31 of the tube 29extends approximately of the circumference of the central opening before passing upwardly to contact the upper Wall 22 and to the outletpipe 26. The tube 29 is electrically connected to the upper wall 22adjacent the upper ends 32 and 33 respectively, but does not makeelectrical contact with the end Wall 23. A second tube 34 is connectedto the pipe 24 and extends down through the anode cavity and back to theoutlet pipe 26 in a manner similar to the first tube 29. The tube 34 isspaced so as to be symmetrical with the tube 29 and on the opposite sideof the annular member 19. As is best shown in Figure 2, a pair of tubes36 and 37 extend upwardly through the central opening formed in theannular ring 19 and have their inlet and outlet ends connected to theheaders 27 and 28 respectively. The tubes 36 and 37 are electricallyconnected to the inner edge of the wall 23 but, as shown in Figure 2, donot engage the upper Wall 22. Strapping strips of conducting material 38connect the upper ends of tubes 36 and 37 together so that they may bemaintained at the same electrical potential. Likewise, straps 39 connectthe lower corners of tubes 29 and 34.

Water is supplied to the inlet rings 24 and 27, and is removed throughthe outlet rings 26 and 28, respectively. Water flows between the rings24 and 26 through the tubes 29 and 34. The vertical portions of thetubes comprise active portions or" the anode and have radio frequencycurrent induced in them during operation. These induced currents tend toheat the active portions and limit the maximum power obtainable from themagnetron. The cooling fluid flowing through the tubes will remove heatfrom them, and thus allow the maximum energy to be greatly increased.

Another advantage of this invention is that the upwardly extendingcathode 13 which has its active portion 14 within the power generatingcavity acts as an antenna, and

normally couples a great deal of energy from the device. It has beencustomary prior to this invention to put external choke coils about thesupport 13 to choke the high frequency energy and thus keep it frombeing lost through the cathode connection. The efficiency of theapparatus, therefore, has not been high. Applicants structure with thehorizontal cross portions of the tubes 29 and 34 and the straps 38 willeliminate this antenna effect. As shown in Figure 2, the cross portionsof the tubes and straps 38 adjacent the upper wall 22 of the annularmember 19 are electrically connected to the lower wall 23 of the annularmember, and thus are maintained at this potential. The upper wall 22 andthe lower wall 23 are 180 degrees out of phase and it is this phaserelationship which normally induces currents in the cathode supports 13.Because of the electrical connection of the straps 38 and the horizontalportions of the tube, the capacitive effect of the end walls 22 and 23will be counter-balanced by the straps 3S and the horizontal portions ofthe tubes. The spacings of the tubes may be adjusted so as to causecomplete cancellation of the antenna effect.

In operation the magnetron illustrated in Figure 1 will run relativelycool, due to the coolant flowing through the inter-digital tubes. Thus,the power output may be safely increased. The output energy is removedfrom the magnetron by the coupling loop 41 in a well known manner. Atthe same time the efiiciency of the tube will be increased because ofthe cancellation of the antenna effect of the cathode support 13 whichis accomplished by the horizontal portions of the tube and the joiningstrips. Since they are connected to end walls which have oppositepolarity, they will tend to cancel the capacitive effect upon thecathode support. Since the horizontal portion of the tubes and thestraps are nearer to the cathode support than are the end walls 22 and23, it is not necessary that they have as large an area or as strong afield as exists between the end walls.

Although this invention has been described with respect to a preferredembodiment, it is not to be so limited as changes and modifications maybe made herein which are Within the full intended scope of theinvention, as defined by the appended claims.

I claim:

1. A magnetron comprising, an annular anode having first and secondaxially spaced walls for terminating a first axially directed electricfield and an outer wall defining a resonant cavity, an axially extendingcathode, said anode and said cathode being coaxially disposed anddefining an interaction space therebetween, means for exciting saidcavity with radio frequency oscillations, a first set of axiallyextending anode segments disposed adjacent the inner periphery of saidannular anode, each of said segments electrically connected at one endto the first of said axially spaced walls and spaced at the other endfrom the second of said axially spaced walls, a second set of axiallyex-.

tending anode segments interdigitally disposed with respect to saidfirst set of segments and electrically connected at one end to thesecond of said axially spaced walls and spaced at the other end from thefirst of said axially spaced walls, means electrically connecting thesaid other ends of each of said sets of segments together, said meansterminating a second electric field directed oppositely to said ofhollow anode fingers being electrically connected at one end to saidfirst wall and being electrically connected at the other end by a hollowportion so that cooling fluid may flow therethrough, said portionextending adjacent the plane of said second wall, with said other endsand said portion spaced from said second wall, said second pair ofhollow anode fingers being electrically connected at one end to saidsecond wall and being electrically connected at the other end by asecond hollow portion so that cool- 7 ing fluid may flow therethrough,said second portion extending adjacent the plane of said first wall,With said other ends and said second portion spaced from said firstwall,

' and means for supplying cooling fluid to said pairs of fingers.

3. In an interdigital magnetron having a central axially extendingcathode and a coaxial annular anode including a pair of axially spacedwalls and being of a generally U shape in cross section, interdigitalmeans comprising a first tube connected to the first wall of said anodeand having a first portion extending axially through the anode cavity, asecond portion extending transversely through the anode cavity and athird portion extending axially through the cavity to said first wall, asecond tube connected to the second anode wall and having a firstportion extending axially through the anode cavity, a second portionextending transversely through the cavity and a third portion extendingaxially to connect to the second anode wall, said first tube spaced fromsaid second anode wall, said second tube spaced from said first anodewall, a first input manifold connected to one end of said first tube tosupply cooling fluid thereto, a first exhaust manifold connected to theopposite end of said first tube to remove the fluid therefrom, a secondinput manifold connected to one end of said second tube to supplycooling fluid thereto, and asecond exhaust manifold connected to theopposite end of said second tube to remove the fluid therefrom.

References Cited in the file of this patent UNITED STATES PATENTS BrownOct. 21, 1952

